Bleeding mechanic should be like for example.
You get 25% opening. This naturally starts decreasing 24.. 23.. and so on.
Each time your character would bleed for 1 hp.
Using defense moves to remove openings wouldnt cause bleeding.
So if you deal 78% opening to animal and it starts running away. It will slowly bleed 78hp one by one. Leaving blood trail to track it as well.